Electric contact



Nov. 7, 1944.

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Vrnm Heil YMMM Patented Nov. 7, 1944 ELECTRIC CONTACT Vernon E. Heil, Indianapolis. Ind., assignor to P. R. Mallory & Co., Inc., Indianapolis, Ind., a

corporation of Delaware Application December 7, 1943, Serial No. 513,231

4 Claims.

This invention relates to electric contacts.

An object of the invention is to improve silver base electric contacts.

Other objects of the invention will be apparent from the description and claims.

lin the drawing:

The figure is a graph of the number of welds between silver contacts containing small proportions oi copper during 50,000 operations in making and breaking an A. C. electric circuit carrying 20, and 30 amperes of current.

Electric make and break contacts have been made of fine silver and also of silver containing several percent of copper such as coin silver and sterling silver. Such contacts have been satisiactory for many applications but have been limited in their current carrying capacity by their tendency to weld together during operation when iairly high currents are carried.

I have now discovered that silver electric contacts containing percentages of copper within the range:

Per cent by weight copper--. 0.85 tu 2.05 ilililver Balance are far superior to fine silver and to silver-copper alloys containing higher percentages of copper ior electric contacts.

Tests conducted on silver contacts containing different percentages of copper show that the welding or sticking tendency of contacts containlng copper in the above range is much less than that of contacts containing either higher or lower proportions of copper. The contact resistance of the silver-copper alloy contacts is also appreclably lower than that of ilne silver. Moreover, when the currents used are sufllcient to cause welding of a pair of contacts together, the force required to separate these silver-copper contacts is much less than that required to separate ilne silver contacts similarly welded. 'I'hus if welding does take place a greater proportion of the welds will immediately pull apart during operation and hence will not seriously interfere with the continued operation of the contacts.

'I'he temperature rise encountered during operation is approximately the same for the silvercopper contacts and for une silver.

In the above critical range the preferred compositions are those containing between 1.08 and 2.05% copper and a preferred specific contact material is one having the composition:

. Per cent copper 1-5 Silver 98.5

Small additions of other elements may be present if they do not adversely affect the properties of the contact materials.

The contacts may be fabricated by ordinary methods such as by melting the silver and copper together and casting followed by rolling, drawing, heading, punching, forming, pressing and assembling to obtain contacts of the desired form, as is now employed in making fine silver contacts. y

The graph shows the results of sticking tests on contact pairs made of silver containing various proportions of copper. Each contact pair was tested for 50,000 make and break operations controlling a current 20, 25 or 30 amperes A. C. respectively from a 115 volt supply. It will be noted that 1100 welds occurred with 30 amperes load during the test period for the ne silver contacts. The weld frequency increased greatly with small additions of copper then dropped sharply to welds at 0.85% copper. Between 0.85 and 2.05% the weld frequency is extremely low after which it rises fairly rapidly.

'I'he tests at 25 amperes showed almost negllgible welding in th range 0.85 to 2.05% copper, the weld frequency increasing rapidly with less or higher copper percentages. At 20 amperes no welding occurred in this range. Where welding occurred the weldstrength was measured and it was found that a range of low average weld strength coincided with the range of low weld frequency.

Contact resistance measurements were also made and, although somewhat irregular over the range covered the lowest resistance material was that containing 1.5% copper and the entire range of 0.85 to 2.05% copper was lower than that of iine silver.

While specic embodiments of the invention have been described, it is intended to cover the invention broadly within the spirit and scope of the appended claims.

What is claimed is:

1. An electric contact containing 0.85 to 2.05% copper, balance silver.

2. An electric make and break contact containing 0.85 to 2.05% copper, balance substantially all sliver, said contact being characterized by less tendency to weld during operation than nne silver and silver-copper alloys containing higher proportions of copper.

3. An electric make and break contact cons l taining 1.08 to 2.05% copper, balance silver.

4. An electric contact containing 1.5% copper. balance silver.

' VERNON E. HEIL. 

